The present invention relates to proteins and peptides which have antiproliferative and/or anti-infective activity. These molecules have been isolated and characterized as part of a research initiative to identify factors responsible for the delicate balance between proliferative and antiproliferative forces which operate during embryogenesis. The research has been based on the theory that pregnancy operates, figuratively speaking, like a reversible cancer, in that like cancer, the products of conception are invasive and penetrate the circulation. Embryonic cells, and their tumor cell counterparts, express similar surface antigens (e.g., alphafetoprotein and carcinoembryonic antigen) and secreted factors. Furthermore, the conceptus, like a tumor, is not rejected by the mother's body, but rather harnesses maternal resources to secure its well-being. Unlike cancer, however, the invasiveness and tolerance associated with pregnancy are reversible at almost any time.
As described in U.S. Pat. No. 5,648,340 by Dr. Barnea, which is incorporated by reference in its entirety herein, agents have been identified which operate to control the development of the embryo such that proliferation, invasiveness and differentiation may occur without substantially injuring the maternal host. It has been discovered that several agents produced by the embryo appear to play an important role in its development. U.S. Pat. No. 5,648,340 discloses the purification of protein extracts having molecular weights less than 10,000 daltons (and particularly less than 8,000 daltons) which have antiproliferative activity and less than 3,000 daltons which exhibit proliferative activity.
The protein preparations described in U.S. Pat. No. 5,648,340 have now been subjected to further analysis, and it has been discovered that proteins from high molecular weight fractions of the extract exhibit both an antiproliferative effect on cancer cells and a broad-spectrum antiviral effect, and that low molecular weight fractions of the extract comprise an active antiproliferative agent which is a heptapeptide having a molecular weight of approximately 820 daltons.
In particular, according to the present invention, the higher molecular weight subfractions of the proteins described in U.S. Pat. No. 5,648,340 were observed to inhibit the proliferation of various types of cancer cells and also the cytopathic effect of a variety of viruses, including viruses of the Retrovirus, Bunyavirus, Togavirus, Reovirus, Herpesvirus, and Poxvirus families. These viruses are structurally extremely diverse and exert their effects through distinct biological mechanisms.
Retroviruses, such as human immunodeficiency viruses types 1 and 2, are RNA viruses which reverse-transcribe their genomic RNA as part of their replicative cycle. In DNA (“provirus”) form, they are able to integrate into host chromosomal DNA, where they can persist for extended periods of time. Bunyaviruses are arthropod-borne viruses which use negative strand RNA as their genetic material. Examples of members of the Bunyaviridae family are Bunyamwera, Uukuniemi, La Crosse, Punta Toro, and San Angelo viruses, and Rift Valley, Sandfly, and Crimean-Congo hemorrhagic fever viruses. Togaviruses are icosahedral, positive-strand RNA viruses, and include numerous viruses which are pathogenic in man. Among the Togaviruses are eastern equine encephalitis, western equine encephalitis, Venezuelan equine encephalitis, Sindbis, Chikungunya, Semiliki Forest, St. Louis encephalitis, yellow fever, rubella, and dengue viruses. Reoviruses are double-stranded RNA viruses which are frequently associated with diarrheal illnesses. In contrast, Herpesviruses and Poxviruses are double-stranded DNA viruses. The Herpesvirus family includes herpes simplex 1 and 2, varicella-zoster (chicken pox), and Epstein-Barr viruses. The Poxvirus family includes variola (smallpox) and vaccinia viruses.
The ability of protein of the high molecular weight fraction of embryonal extract to inhibit the cytopathic effect of viruses from each of these families of viruses as well as the proliferation of various types of cancer cells suggests that it exerts a generally protective effect on cells which is part of the biologically privileged status of the developing embryo.